Not sure where you are based but in Cornwall there is a new full on Jump Park / Biker X park with many runs, jumps, berms ect. its been said its one of the best in the UK. Its on the road between Redruth and Portreath (nice seaside village with an excellent beach / surfing) As for just trails, where do you start! Cornwall is riddled with them. The coast path between Portreath and Perranporth is extreme in itself as a route plus there are many many wooded areas with some fantastic downhills route.... trust me Ive done them!
If you need any further info on Cornwall just ask...especially if it involves bikes and cycling!